Bisphenol compounds, including Bisphenol A (BP A), are widely used as building blocks for a variety of commercial, industrial, and military products. Specifically, bisphenols are the building blocks for polycarbonate plastics, epoxy resins, polyester resins, and cyanate ester resins for example. BPA-derived plastics have been commercially produced since the 1950s, and have become important because of their shatter resistance, thermal resistance, electrical resistance, and optical clarity. Polycarbonate plastics are found in a wide range of products, including eyeglass lenses, CDs and DVDs, computers, appliances, power tools, sports equipment, medical devices, as well as food and drink containers. Epoxy resins are easily formed from BP A and are resistant to chemicals, which makes them useful in products such as printed circuit boards, paints, adhesives, and coatings for the inside of metal cans. While polycarbonates and epoxy resins are the major applications for bisphenol A, other uses include flame retardants, unsaturated polyester resins, polysulfone resins, polyetherimide resins and polyarylate resins.
More than 850,000 tons of BP A were consumed in the U.S. in 2003; 72% of which was used to make polycarbonate plastic and 21% going into epoxy resins. During 2013-2018, the total world consumption is expected to grow at an average annual rate of 4.2%. Currently BP A is synthesized by the condensation of acetone (signified by the suffix A in the name) with two equivalents of phenol. The reaction is catalyzed by a strong acid, such as hydrochloric acid (HCl) or a sulfonated polystyrene resin.
Commercially available bisphenol compounds, especially polyaromatic bisphenols, are derived from petroleum, a limited resource. What is needed is a renewable source of these bisphenol compounds to meet the growing demand. Research into bio-derived materials for plastic and resin precursors is extremely active. The current invention provides a renewable, bio-derived source for BP A and analogues. In an effort to create more sustainable bisphenol building blocks the current method provides for the selective synthesis of bisphenols from salicylic acid, the major component of wintergreen oil, and a viable target for engineered biosynthesis. As a tangential benefit, renewable phenols may have significantly lower toxicity than typical precursors of bisphenol A.
U.S. Pat. No. 5,770,658 (Baudoul, et al.) describes the reaction of an epoxy resin with an alkyl or alkenyl substituted hydroxyl substituted aromatic acid (e.g. salicylic acid) or compounds derivable from salicylic acid (such as cresol) to produce resins for coating and civil engineering applications. U.S. Pat. No. 5,936,057 (Baudoul, et al.) similarly describes epoxy resin mixtures with alkylated salicylic acid. These patents describe the use of salicylic acid to modify resins but not the direct use of salicylic acid as the starting product to make polyphenols and their resulting plastics and resins.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the invention, as claimed. Further advantages of this invention will be apparent after a review of the following detailed description of the disclosed embodiments, which are illustrated schematically in the accompanying drawings and in the appended claims.